Prof.MacQueen

1

Lecture 7 Lecture Summary In this lecture will continue the text’s discussion of bipedalism. This lecture will also provide some further information on the early hominids: Ardipithecus, Australopithecus, and Homo and their associated biocultural evolution. Bipedalism Perhaps the most crucial change in early hominid evolution was the development of bipedal locomotion – walking on two legs. We know from the fossil record that other important changes such as the expansion of the brain, modification of the female pelvis to allow bigger-brained babies to be born, and significant reduction of the face, teeth, and jaws, did not occur until about 2 million years after the emergence of bipedalism. Be familiar with the specific anatomical features associated with bipedalism as described in chapter 6 of your text. Why did we evolve to become bipedal? There are at least 6 different models that have been proposed to account for the evolution of bipedalism:

1.) Carrying model – bipedalism could have allowed our ancestors to search for and collect food in greater safety and with greater efficiency by freeing the arms and hands. Mothers could carry their children. They could carry sticks and rocks to throw at predators and scavengers.

2.) Vigilance model – bipedalism, by elevating the head, helped our ancestors locate potential food sources and dangers. This behavior is seen in other animals, squirrels and apes, but says more about upright posture than it does of actual locomotion.

3.) Heat dissipation model – the vertical orientation of the body in bipedalism helps cool the body by presenting a smaller target to the equatorial sun rays and placing more of the body above ground to catch cooling air currents. This model applies to hominids in the hot savannah but not so much in the shady forested areas.

4.) Energy efficiency model – bipedalism is an energy-efficient way of running and walking compared to quadrapedalism. Long periods of steady bipedal walking in search of food would seem to require less energy but the first hominids may not have walked quite like our more recent ancestors-they may have walked in a way more similar to chimps. So, it has been proposed that bipedalism may have had other advantages first and then further anatomical changes made it more energy efficient.

5.) Foraging/bipedal model – this model suggests that standing upright provided the benefit of reaching in bushes and trees, particular ones that were difficult to climb.

6.) Display model – bipedalism is thought by some to have emerged as a way to exhibit an upright display posture like that seen in chimps (and bonobos) during dominance confrontations. An upright display conveys meaning because it makes the individual seem larger and is directly related to mating success.

2

All of these models have some supporting evidence and it would not be absurd to assume that perhaps some or all of them worked together to play a role in the emergence of bipedalism. However, those models that explain why hominids would have more reproductive success probably played the most important role - as you recall that is the measure of natural selection. Whatever the cause, bipedalism is the trait that distinguishes the hominids from other primates. The First Hominids Within the family Hominidae, anthropologists now generally acknowledge at least 3 well-established genera: Ardipithecus, Australopithecus, and Homo. Of course only the last genus still exists; the others are long extinct. Ardipithecus Ardipithecus were the most ape-like hominids. Dating to 4.4 million years ago (mya), Ardipithecus ramidus is considered a hominid because the hole in the skull for the spinal cord (foramen magnum) is positioned more forward than in apes, indicating a more bipedal locomotion. But the large canine teeth and other features distinguish it from later hominids. It seems that it is very close to the time when hominids and apes split and may be, as its name implies, the “root” hominid species. Another relatively new species emerged in 2004 called Ardipithecus kadabba. Found in the same Ethiopian locale as ramidus, kadabba dates to 5.8 to 5.2 mya. The toe bone is angled in such a way as to suggest habitual bipedalism at a very early date. The interpretation of these fossils has been controversial, however, and not everyone agrees that they should be placed in the Ardipithecus genus – some authorities think they are chimp ancestors. Australopithecus There are two groups of australopithecines. One set of Australopithecus is small-brained, gracile (slender), with a mixed vegetable/fruit diet. Another set of Australopithecus is small-brained, robust, with a grassland vegetable diet. Some authorities think that the difference between the two groups is great enough to warrant a separate genus called Paranthropus (for the robust group). The authors of your text are “lumpers” in this case and don’t recognize a fourth genus of hominids so we will use their taxonomy. Australopithecus anamensis The oldest, Australopithecus anamensis, dates to 4.2 to 3.9 mya. Found only in northern Kenya, they, too, exhibit ape-like features such as large canines and parallel tooth rows along with more human-like features such as thick molar enamel. Their leg bones are clearly those of a biped. Australopithecus afarensis Lucy (possibly our most famous human ancestor-named for the Beatles song) was the first specimen of Australopithecus afarensis discovered in 1974 and dating to 3.2 mya. For more on Lucy’s story: http://www.asu.edu/clas/iho/lucy.html

3

Afarensis more generally dates to 3.9–2.9 mya. Living off a diet of fruits, nuts, seeds, and tubers, the species is restricted to East Africa and is known for being quite sexually dimorphic. Their brain size is very similar to apes (380-500 cc), the face is projecting, their canine teeth are smaller than apes but they have ape-like features like parallel tooth rows and relatively long arms. The curved finger and toe bones, shortened pelvis, and femur angled over the knee are some of the features that demonstrate they were bipedal.

Laetoli footprint (left). Knee joint (right) from Hadar, Ethiopia (where most of this species is found including Lucy) showing a habit of walking.

A composite reconstruction of A. afarensis from Hadar, Ethiopia (left) and jaw showing ape-like features such as the u-shaped dental arcade (right). Australopithecus africanus Australopithicus africanus dates to 3-2.3 mya. These fossils are mainly from South Africa although some have been found in Kenya and Ethiopia. Their body size and shape

4

and brain size (435-530 cc) is similar to afarensis but their faces are less projecting (prognathic) and they lack the ridge lying longitudinally along the skull (sagittal ridge). Their canine teeth are smaller and the tooth rows are more rounded than parallel, i.e. closer to humans than apes. There is some evidence to suggest that these australopiths (afarensis and africanus) hunted small animals or scavenged carcasses of larger ones. Carbon isotope analysis of tooth enamel shows that they either ate tropical grasses or ate animals that ate tropical grasses, or both. Because the teeth do not show signs of wear consistent with eating grass researchers are more apt to believe they were eating meat. The similarity of the two species suggests a plausible interpretation that A. africanus is a continuation of A. afarensis showing some evolutionary changes (one hypothesis).

Australopithecus afarensis: “Taung baby” (left) and “Mrs. Ples” (right) found in South Africa. Australopithecus garhi The site of Bouri, in Ethiopia, dated to 2.5 mya has revealed bones of hominids and bones of antelopes, horses, and other animals with cutmarks made by stone tools. The hominid and animal sets of bones are found in different locations within the site but whoever the hominid was, they were butchering the animals for meat and potentially smashing the bones to get at the fat-rich marrow. The cranial bones are similar to A. afarensis (e.g. they have a prognathic jaw and similar brain size) but they also share features with early Homo (e.g. the relative length of legs are arms)–leading researchers to believe it was a new species, A. garhi. The evolutionary relationship of garhi to other hominids is still a matter of debate. Its discoverers feel it is descended from A. afarensis and is a direct ancestor of Homo. Australopithecus aethiopicus

A. aethiopicus (sometimes called Paranthropus aethiopicus) dates to 2.8-2.2 mya. The original fossil, called the Black skull due to the stain from minerals in the soil, was found in Lake Turkana, Kenya. The Black Skull has the smallest adult

5

brain, most prognathic face, and largest sagittal crest of any well-established hominid. In general, these fossils were considerably more robust than the gracile forms in those features involved with chewing. These large cranial features point to a diet of large amounts of vegetable matter emphasizing seeds, nuts, hard fruits, and tubers. This is confirmed with microscopic wear on the teeth. Fossils of this species have also been found in Ethiopia.

KNM WT 17000 or “Black skull” from Kenya with both derived and primitive traits. Australopithecus robustus A. robustus was found in South Africa and dates between 1 and 2 mya. Like aethiopicus it retains the body size of the gracile australopiths but there is a slight increase in brain capacity. The jaws are heavy, the back teeth are large, and there is a sagittal crest-all indicating a mixed, tough, vegetable diet. But the crania are not as robust as aethiopicus.

A. robustus: SK 48 (left) and SK 46 (right)

Sagittal Crest

6

Australopithecus boisei A. boisei was found in Tanzania, Kenya, and Ethiopia and existed between 1.2-2.3 mya. Boisei shows features that, along with aethiopicus, are sometimes referred to as “hyperrobust”. “Zinjanthropus”, found by the infamous Leakeys, was the first specimen of the species found. Dubbed “the nutcracker man”, this specimen has extremely large jaws and back teeth with a large sagittal crest.

A. boisei: “Zinj”. Putting it all together As stated in your text, the relationship among australopithecines and their relationship to Homo are still debated by anthropologists. Most would agree that the robust forms represent a separate evolutionary dead end branch and that at least one of the more gracile forms led to the genus Homo. Please refer to pg. 140 of your text. Homo When the Leakeys discovered the robust australopithecine, Zinj, they also found stone tools at the same level as the fossils. They felt that Zinj was too primitive to make these tools in this time period called the Lower Paleolithic (or early stone age). The tools, called Oldowan (from Olduvai gorge where they were found) are simple pebble tools: water-worn cobbles 3-4 inches in diameter that have been modified by knocking off flakes from one or two sides to make a sharp edge. More recent research suggests that even at this time hominids may have been utilizing the flakes (in addition to the cores) for such tasks as cutting meat and plant material, scraping meat off bone, and sawing wood or bone. Microscopic analysis reveals polish along the edges of the flakes that indicate these kinds of use.

7

Oldowan tools from the University of California Berkeley Collection and University of Indiana Collection/Lithic Casting Lab. There has been some relatively new research suggesting that australopiths may have manufactured stone tools but the majority of evidence, and that which is accepted by the scientific community, is that the first hominid to manufacture tools were members of Homo habilis (“handy man”). Homo habilis/Homo rudolfensis Homo habilis shows an increase in brain size from the earlier australopithicine genus. The presence of stone tools indicates that these larger brains were capable of a complexity of thought not seen previously marking a beginning of a new trend in hominid evolution. Dating to 2.3-1.6 mya, H. habilis has been found in Tanzania, Kenya, Ethiopia, and perhaps southern Africa. Like australopiths, their taxonomic affiliations are not yet agreed upon. Fossils from east Turkana, Kenya are different enough to be considered a separate species, Homo rudolfensis. Rudolfensis has a larger body and brain size than habilis and lacks the continuous brow ridge existing over the eyes. Others believe that they are still a single species, habilis. The limb proportions of both of these early Homo species resemble A. africanus more than any other australopith. This is why africanus is usually argued to be the direct ancestor to our genus. Early Homo, it is hypothesized, lived in small cooperative groups, possibly families, foraging in mixed grassland/woodland areas for plant food and carnivore kill. Their big brains allowed them to better understand and manipulate their environment, making

8

creative and technologically advanced stone tools that allowed them to process the carcasses they found and take them back to a safe place to finish the job. It was likely a harsh life, but they were successful. The adaptive abilities of bipedalism, large brains, social organization, and tool technology set the course for the rest of hominid evolution.

Homo habilis (OH 24) and Homo rudolfensis (KNM ER 1470) Homo erectus In 1891 the first fossils of Homo erectus were discovered in Java. At the time most people thought that humans had first evolved in Asia, despite Darwin’s suggestion that Africa was the birthplace. When Eugene Dubois found a skull cap and diseased femur that he thought represented the “missing link” between apes and humans, he called it Pithecanthropus erectus, popularly known as Java man. Since then numerous similar fossils have been found in java and they are now recognized as belonging to our genus but a different species, Homo erectus. H. erectus in this region is similar to H. erectus on Asia and Africa except that their average brain size is often larger. Some of the more famous and numerous erectus fossils come from Zhoukoudian, a cave outside of Beijing, China dating between 460 and 230 kya. In addition to the hominid fossils, stone tools and animal bones have also been found. New evidence suggests that most of the H. erectus bones in the cave were the remains of hyenas’ meals. Part of the fame associated with Zhoukoudian lies in the fact that the Peking Man went missing. When the Japan invaded China in 1937, U.S. Marines attempting to get the fossils out of the country were captured by Japanese troops. The fossils have been missing ever since but this happened after measurements and casts of the bones had been made. It should be mentioned that the oldest fossils of this group found in Kenya are considered by some to be a separate species, Homo ergaster (work man). In some ways these are typical of Homo erectus from Asia: heavy brow ridges, prognathic face, sloping forehead, elongated profile, sagittal keel, and sharply angled occipital bone with a pronounced bony ridge (torus), and similar cranial capacity. In other ways they differ: the bone is thinner with smaller facial bones. These modern looking features are what led to its placement in

9

the species H. ergaster. However, your text treats these fossils the same, referring to them as H. erectus. From the neck up, Homo erectus/ergaster is quite distinct from early Homo (habilis/rudolfensis) in overall size, ruggedness, and particularly brain size. The skull still retains primitive features that distinguish it from modern Homo sapiens.

Homo erectus skull cap (Sangirin 2) and Homo ergaster (KNM ER 3733) According to recent data, H. erectus reached China and Southeast Asia by at least 1 mya and perhaps as much as 1.8 mya. What prompted them to leave the savannas they seemed so well-adapted for? We don’t know for sure but some think it is because of their reproductive success. Their big brains allowed them to exploit the savannas more so than any of the earlier species of Homo. They had better and more variable tools (discussed below) and an increased ability to learn about their environment and face the challenges in it. They also likely had a more complex social organization. With these adaptations, H. erectus would have rapidly increased in population size. With increase in population size, however, comes competition for resources and pressure on social groups. This may have prompted H. erectus to move outside the familiar region to seek out new resources such as food, water, and shelter. Thus, they moved to China, Indonesia, and perhaps Europe, where they were eventually confronted with new selective pressures of the Pleistocene, in particular a drop in worldwide temperature. What’s different about the H. erectus brain? Although it is larger than early species of Homo, it was not disproportionately larger than expected given their larger body size. Although the brains themselves are not preserved, a cast of the brain (endocast) can be made from the existing skull. Endocasts made from H. erectus are similar in some ways to Homo sapiens. Like modern humans, their brains were asymmetric-because of the specialization of the differing hemispheres (we see this also in Old World monkeys and chimps). Some research indicates that H. erectus possessed linguistic skills and the ability to manipulate symbols, along with hand-eye coordination similar to ours. Not everyone is convinced. But their brain seems to be associated with several important innovations: tool manufacture, controlled use of fire, cooperative hunting, and language. While we still see some of the simple pebble technology associated with H. erectus, we more often find a sophisticated toolmaking tradition called Acheulean where the end

10

result is a hand axe. A hand axe is a symmetrical, edged, pointed, bifacially flaked tool that may have served many purposes-piercing animal flesh, scraping hides, cutting wood, digging roots. That the Acheulean tradition evolved from the Oldowan, seems clear. Oldowan choppers found in South Africa resemble crude hand axes. Acheulean tools arrive in Africa at about 1.4 mya, spread to Europe, and continue to the Upper Pleistocene. Though, hand axes are commonly found in Africa and Europe, they are absent from most H. erectus sites in Asia east of India. This dividing line is so clear that it has been called the Movius Line (named for the researcher who first articulated it). The fact that hand axes don’t exist east of the line, doesn’t necessarily mean that these hominids were less advanced. Perhaps there was a lack of suitable stone or they relied on other material; some have suggested that bamboo may have been utilized for a similar function as the hand axe. The line may also suggest that hominids left Africa and arrived in East Asia before the hand axe was first developed in Africa.

The Movius Line. The ability to control fire is significant: providing heat and light, protection from predators, and the ability to cook food. Your text provides a few examples of the earliest use of fire but there are more possibilities, some dating to 1.6 mya in Kenya and China. Similarly, your text points out only a couple of the sites that reveal evidence of hunting. Seasonal hunting camps where groups of individuals came together to hunt, socialize, and exchange information are potentially found in Spain, Kenya, and Tanzania. The sites have large concentrations of prehistoric animals that appear to have been stampeded or driven into a swamp, where they were then killed and butchered. In some cases stone tools are found in association with the animal bones. If the interpretations are correct, we can infer a high level of knowledge, cooperation, and coordination among hominids living several hundred thousand years ago. Despite the fact that Homo erectus is now extinct, it was certainly a success. Evolving nearly 2 mya in Africa, possibly from an earlier species (Homo ergaster) and spreading as far as Java by 1.8 mya, reaching China and Europe by 500 kya, and lasting in Africa

11

and China until 250 kya, their adaptations clearly allowed them to exploit a number of different environments. Weekly Readings Summary Wilson 2007 This week wraps up the Wilson book with chapters 31-36. Here he provides another example of large groups in culture functioning as a collective unit – nations. And he reiterates, behavioral diversity can be studied like biological diversity.